This invention relates mainly to the offshore oil industry. Operation of a typical offshore drilling platform requires supply of many tons of various materials daily. These materials are delivered mainly by supply boats to the platform and lifted from the boat by platform's stationary crane. This operation requires relatively fixed position of the supply boat near the platform. Rough weather conditions during which many of the platform's re-supplies must be done, complicates this operation. Presently, in most of the cases, the supply boat is moored to the platform by two mooring lines, connected to their stern part and by bow anchor, which tensions the mooring lines, locating the supply boat on the same distance from the platform's structure and preventing it from free movement. This mooring system successfully protects the supply boat from collision with the platform's structure but practically excludes the use of any gangway for transporting perconnel, thus leaving the platform's crane as the only means for transporting the personnel.
The system is known (U.S. Pat. No. 4,003,473) which uses a ramp (gangway) as a mooring element, thus providing stable connection for personnel between supply boat and platform. This system did not find wide use because it is permanently located on the relatively low height from water level and therefore is subject for destruction during severe storms.
In both mentioned systems the supply boat uses its bow anchor for orientation and tensioning mooring lines. In the cases when the offshore platform is locaed in deep water, the anchor can not be used. In these cases the supply boat uses its engine and propeller to create a trust sufficient to tension the mooring lines.